Data redundancy is used in data storage systems to protect customer's data against individual component malfunction. If any data portion stored in the system is stored in two or more separate physical copies located at separate components, such as disk drives, then data will not be lost if one of these components fails or malfunctions, since the host can still obtain the requested data from the remaining copy or copies. Mechanisms for ensuring and maintaining data integrity are implemented in such systems.
One approach used for preserving data integrity is known as “scrubbing”, typically embodied in software applications that run as background processes and check that all existing copies of data portions are correct and can be safely read. If any copy of the data is unavailable, corrupted, or inaccurate, it is then corrected, typically by being overwritten with data taken from readable and correct copy or copies of the data.
In the known art, scrubbing processes are typically implemented by systematically scanning all data stored in the system, in cycles that may take one or more week before being completed. On the other hand, data that was recently modified is more likely to become corrupted or unavailable.
There is therefore a need for procedures that ensure data integrity in mass storage systems which attend more frequently to data portions that are more likely to be corrupted or unavailable.